Referring to FIG. 1 of the drawings, the reference numeral 100 generally designates a conventional monolithically integrated or “on-chip” thermocouple. Thermocouple 100 generally comprises a membrane 102 that includes two different thermally conductive materials 110 and 112 that extend from the silicon substrate 104 (which is typically referred to as a “rim”) over a recess 108 formed in silicon substrate 104. As heat or infrared radiation is applied to the membrane 102, a temperature differential is created in the membrane 102 between the area over the recess 108 and the “rim” (where the substrate 104 operates as a heat sink). Many of the thermocouples 100 can then be arranged into a thermopile so as to be able to ascertain readable and reliable temperature measurements.
Thermocouple 100, however, has numerous drawbacks. First, the deep selective etching used to form recess 108 is a non-standard manufacturing step, which can dramatically increase the manufacturing costs. Second, the membrane 102 is very fragile, which generally requires special handling and packaging and which generally makes the membrane sensitive to pressure and vibration. Additionally, because of the fragility of the membrane 102, the size of the membrane is mechanically limited.
Turning to FIG. 2, another, alternative thermopile 200 can be seen. Thermopile 200 generally comprises a first set of materials 202-1, 202-2, 202-3, and 202-4 and a second set of materials 204-1, 204-2, 204-3, and 204-4 arranged in a “serpentine” on a silicon substrate 104. As air (or another fluid) traverses the thermopile, a temperature or thermal gradient is formed across the thermopile 200. While the arrangement of thermopile 200 is more mechanically durable than a thermopile having an array of thermocouples 100, thermopile 200 has very low sensitivity and generally requires a large amount of area, making it prohibitively expensive.
Some other examples of conventional thermocouples and thermopiles are: U.S. Pat. No. 3,393,328; U.S. Pat. No. 5,059,543; U.S. Pat. No. 5,343,064; U.S. Pat. No. 6,531,899; U.S. Pat. No. 6,565,254; U.S. Pat. No. 6,793,389; U.S. Pat. No. 6,987,223; U.S. Pat. No. 7,042,690; U.S. Pat. No. 7,282,712; U.S. Pat. No. 7,406,185; U.S. Patent Pre-Grant Publ. No. 2009/0260669; Paul et al., “Thermoelectric Infrared Imaging Microsystem by Commercial CMOS Technology,” Proc. Eur. Solid-State Device Conf, Bordeaux, France, Sep. 8-10, 1998, pp. 52-55; and Lahiji et al., “A Batch-Fabricated Silicon Thermopile Infrared Detector,” IEEE Transactions on Electron Devices, Vol. 29, No. 1, January 1982 pp. 14-22.